Alternating current is the standard for power sources. However, many electrical and electronic devices require direct current power supplies. To address this need, power conversion is performed. Power conversion often involves both converting an alternating current source to a direct current as well as scaling the magnitude of the signal to an appropriate level.
Ethernet devices, such as Ethernet switches, computers, and other devices generally require a 48 volt direct current signal. In addition, this signal is often current-limited to meet Ethernet standards. Some Ethernet devices can accommodate in-line power, meaning an associated Ethernet switch provides power in conjunction with the providing of data to the Ethernet device. Other Ethernet devices, often referred to as legacy devices, do not accommodate such in-line power, and utilize separate power sources.
Conventionally, in Ethernet applications, power conversion involves two power conversion stages. The first is often referred to as a power factor correction stage in which an 85 to 265 Vrms alternating current signal is converted to a constant 400 volt direct current signal. The second stage provides isolation from the alternating current line and converts the 400 volt direct current signal to an output voltage of 48 volts DC. An in-line power detection circuit adds a third stage for Ethernet applications involving both legacy and in-line power compatible devices. The use of three stages to convert from an available alternating current signal to an Ethernet in-line power signal often requires too much equipment volume, is inefficient, and is costly.